A bent electrode is almost always caused by a foreign object in the cylinder. Assuming it was straight before it was installed of course. Maybe something fell in intake during reassembly. At first it might wedge in a valve and cause your lash pad to fall off. Then it would get past the valve and bang around in the cylinder. Could bend a valve or punch a hole in the piston. You can imagine that's not good. If you have a way of pressurizing the cylinder with air you can listen at the exhaust pipe, intake, and the oil fill on the valve cover to determine if and what might be leaking compression. You need the cylinder to be at the top of the compression stroke. And a way to hold the crank from spinning when you pressurize. In gear with the brake on and wheel chocks will work, just don't use 150 PSI. A little goes a long way.

Steve

Edited December 30, 200816 yr by doradox
piston

Ok, thought I would post a Z update and would like to some comments.

I went back and took the valve cover off again and another lash pad had fallen off. Different one this time. I figured this was caused becaused I may have adjusted the valve to loose or something was really wrong. So I did another vavle adjustment and I can tell i'm definately getting better at it. Turning crank over by hand was better than bumping the starter. Made sure each lobe was pointing directly up when I adjusted. Double and triple checked adjustments after I tightend the lock nut. It seemed like everytime I would tighten it would change the lash setting. So I made sure all were correct and took my time and pretty darn sure I did it right this time. Turned on the car and it seem to run better than its ever run. Idle is a little lower than it was. It was at around 100rpm now its at around 800rpm. Runs smooth!

So I drive it around a couple of times and everything is still smooth. I'm scared to really push it, because before it would run good and then I would push it and the lash pad fell off. I also put some Marvel Mystery Oil in it because I could see some sludge around the valve springs and I figured it couldn't hurt.

I've been slowly pushing her and have gotten her to 4500rpm with no problem. I also bought a Engine compression tester and all 6 Cylinders read 135psi. Seems kinda low but all are exactly the same.

So what do you think. I'll probably go out and push her a little harder tomorrow to see how she takes it.

Another Z update. She has been running fine for about a week now. Seems like the reason my lash pad fell off was because my Z needed a valve adjustment and it had been sitting for a little while.

Atleast thats what i'm hoping! So far so good. Its definately running better after properly adjusting the valves.

Good news, you may have gotten lucky......no major repairs to make.

Mike

Another Z update. She has been running fine for about a week now. Seems like the reason my lash pad fell off was because my Z needed a valve adjustment and it had been sitting for a little while.

Atleast thats what i'm hoping! So far so good. Its definately running better after properly adjusting the valves.

that is good to hear, in the absence of a smoking gun in mine I think I will give valve adjusting one more shot.

Putting all that stuff back together without finding the root cause of zero compression will be utterly frustrating if the problem returns! Great hands-on experinece but if you are time-limited you may be better off pulling the head and have some knowledgeable machinist check out your head for issues.

You may have a "sticky-valve" syndrome that others have mentioned that can eject lash pads?? Only other thought is to check the intake and exhaust valve springs on that dead cylinder to insure they are not broken or have hairline cracks that will impact the amount of force they generate when compressed?

Pulling head requires removal of timing chain sprocket from cam and you must shim the chain with that special shaped piece of plastic to insure the chain tensioner does not pop( you can borrow the one I have). If it does you will need to pull the front cover. If your racing buddies don't have a trustworthy machinist you might consider Bill DiCondino who owns Extreme Cylinder Heads in Palm City. He did great job on my head but he is not cheap and don't be in a hurry.

Check out this sight. http://www.atlanticz.ca/zclub/techtips/ It is the best I have seen for teaching valve adjusting. It even comes with a free movie.

I cant seem to find such a video on that site. Anyone know where its at :-) I would like to actually see it being done.

Thanks

thought it was there, myself...

Edited April 16, 201113 yr by Willoughby Z

Here's a pretty good annotated slide show...

http://www.picturetrail.com/gallery/view?p=999&gid=1803105&uid=786489

Before you take the head off run some cleaner through the intake and see if you can get pressure after that. Also on your compression test did you pull all the plugs, and is the starter good, because 200psi is low you should be closer to 250psi for a 71? If you pulled the plugs you might be ready for a rebuild.

I would have thought 200 psi would be good, but a moot point for me, as I made the decision to go deep on the Z, I am almost done completely tearing it down to take it to the body shop.

I did take the head off and found what looks like 3 pistons that hit the valves

Piston 4

Piston 5

Piston 6

Engine is out

More pics on the link in my signature

The good news is the pistons might be reusable if not crack makes sure you test for cracks. I see a lot of carbon so I would imagine the valves could have been stuck open from that.

This is why I was told with these cars to check and make necessary adjustments every year and I have religiously.